/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        
        ListNode* cur=head;
        while(cur && cur->next){
            int val=cur->val;
            ListNode* pre=cur;
            cur=cur->next;
            while(cur && cur->val==val){
                cur=cur->next;
            }
            pre->next=cur;
        }
        
        return head;
    }
};
